This invention relates to a gas generating composition having an improved thermal stability of a gas generating agent which becomes an actuating gas in an air bag system installed in automobiles, airplanes and the like for protecting human bodies.
Further, this invention relates to a method of using the gas generating composition, a gas generator using the gas generating composition, and an inflator system using the gas generator.
In the existing air bag system, a gas generator is housed in a steering wheel of a driver side or in a dashboard of a passenger side. Since an inside of a car has a considerably high temperature in midsummer, a gas generator is likewise exposed to a high temperature. Further, since a life of a car is considered to be approximately 10 to 15 years, a performance of the generator has to be secured at least within this term. In order to stabilize the performance of the air bag system under such conditions, it is important that the gas generating agent in the gas generator is not deteriorated. When the gas generating agent is deteriorated due to heat or the like, a burning behavior of the gas generating agent changes, and an inflating behavior of the air bag changes accordingly, impairing a reliability of the air bag system.
Generally, a thermal stability of a gas generating agent is closely related with a decomposition temperature. When a decomposition temperature is high, a thermal stability tends to be good. Since a sodium azide based gas generating agent is basically formed of an inorganic substance, it has a high decomposition temperature and a thermal stability. However, since a fuel of an organic material is commonly used in a non-sodium azide based gas generating agent, a decomposition temperature is naturally decreased, and the thermal stability tends to be worse than that of the sodium azide compound gas generating agent. Actually, the sodium azide based gas generating agent starts decomposition above approximately 400xc2x0 C., whereas the non-sodium azide based gas generating agent mostly has a decomposition starting temperature of not higher than 250xc2x0 C. The evaluation of these thermal stability is determined depending on the type and the composition ratio of components contained in the gas generating agent. Thus, it is difficult to improve the thermal stability without changing the type and the composition ratio of the gas generating agent.
JP-A 8-12481 discloses that with respect to a method of preventing decomposition of a gas generating agent and improving a thermal stability, in order to prevent decomposition caused by contact between azodicarbonamide (ADCA) and CuO as an oxidizing agent, one or both thereof are subjected to surface coating treatment. However, with a composition of ADCA/KClO4/CuO/starch shown therein, a combustion temperature is too high, so that a filter of a gas generator or an air bag is damaged with heat, or a particulate KCl mist generated by the gas generating agent after burning is released outside the gas generator in a large amount. Accordingly, it is hardly used directly as a gas generating agent for an air bag. In order to solve these problems, a method is considered in which a part of KClO4 as an oxidizing agent is replaced with a nitrate such as KNO3 or Sr(NO3)2. However, in such a modification, a satisfactory thermal stability cannot be provided by the method described in JP-A 8-12481. The reason is considered to be that since KNO3 or Sr(NO3)2 is dissolved in water, starch as a surface coating agent is incorporated in KNO3 or Sr(NO3)2, with the result that the surface of ADCA or CuO is not coated well.
U.S. Pat. No. 5,841,065, DE-A 44 11 654 and WO-A 98/23558 also disclose a gas generating agent.
Accordingly, it is an object of this invention to provide a gas generating composition in which a thermal stability of a gas generating agent containing a non-sodium azide based fuel can be improved without changing a type and a composition ratio of a gas generating agent itself.
Another object of this invention is to provide a method of using the gas generating composition, a gas generator using the gas generating composition and an inflator system using the gas generator.
The present inventor have conducted investigations on a decomposition mechanism of ADCA and other gas generating agents. They have consequently found that the decomposition of ADCA occurs indeed due to contact with CuO, but not only that but also substances such as CONH2 radical, NH2 radical, CO and ammonia generated due to the decomposition of ADCA further accelerate the decomposition, and further that the thermal stability can markedly be improved by removing these decomposition-accelerating substances, and have completed this invention.
That is, this invention provides a gas generating composition characterized by comprising a gas generating agent containing a non-sodium azide based fuel and an oxidizing agent, and an adsorbent.
Further, this invention provides a gas generator characterized by using the gas generating composition.
Still further, this invention provides an inflator system characterized by using the gas generator.
In this invention, as stated above, in the gas generating composition, substances accelerating the decomposition of a fuel, such as radicals, ammonia and the like generated by the decomposition of a fuel, are adsorbed and kept on the adsorbent. Accordingly, since further decomposition of the fuel is inhibited by such a function, the thermal stability of the gas generating agent can be improved. It is therefore possible to improve the reliability of the gas generator and the inflator system and to maintain a stable performance over a long period of time.